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Abstract

Large-area surface ripple structures of indium-tin-oxide films, composed of self-organized nanodots, were induced by femtosecond laser pulses, without scanning. The multi-periodic spacing (∼800 nm, ∼400 nm and ∼200 nm) was observed in the laser-induced ripple of ITO films. The local conductivity of ITO films is significantly higher, by approximately 30 times, than that of the as-deposited ITO films, due to the formation of these nanodots. Such a significant change can be ascribed to the formation of indium metal-like clusters, which appear as budges of ∼ 5 nm height, due to an effective volume increase after breaking the In-O to form In-In bonding.

Figures (8)

(a)–(f) show the SEM images of periodic surface structures induced by 800 nm fs laser pulses at a fluence of 0.1 mJ/cm2 and with various pulse numbers (N = 0, 5×103, 2.5×104, 1×105, 3×105, and 3×106, respectively). The black-square inset shows the enlarged surface features at corresponding locations of (f). The red-square inset shows the 2D Fourier-transformed pattern and its cross-section profile at corresponding locations of (f). The arrow indicates the direction of the laser polarization.

(a1)–(c1) The topographic images and (a2)–(c2) their corresponding surface current images of ITO films induced by 800 nm fs laser pulses with various pulse numbers (N = 0, 3×105, and 3×106, respectively) at a fluence of 0.1 mJ/cm2. (d1) Cross-section analysis on the height along the solid line in the AFM image (c1). (d2) Cross-section analysis on the current along the solid line in the CAFM image (c2).

(a) The first derivative (dN/dE) of AES peaks, In(MNN), Sn(MNN), and O(KLL) as measured for the as-deposited ITO and fs laser treated ITO films. The point A (outside of dot) and point B (inside of dot) correspond to the spots as marked in the SEM top-view image (b) of a fs laser treated ITO film. The red-square inset shows the 2D Fourier-transformed pattern at corresponding locations of (b).

A schematic illustration for the formation of self-organized nanodots induced by the constructive interference of fs laser at near-surface region. The dot is composed of In-rich clusters with height ∼5 nm as a result of In-O bonding breaking into In-In under local-field enhancement.